Optical discs such as CDs and DVDs, for which red semiconductor laser is used, have been widely used as information recording media for recording digital data (information). Examples of the optical discs include: an optical disc in which data is unrecordable and unrewritable (ROM optical disc); an optical disc in which data is recordable but unrewritable (recordable optical disc); and an optical disc in which data is rewritable (rewritable optical disc).
Information is recorded on an optical disc by irradiating laser light to a recording surface of the optical disc. A portion of the recording surface of the optical disc to which laser light is irradiated increases its temperature, which changes an optical recording medium constituting the optical disc. The change of the optical recording medium forms a recording mark on the recording surface of the optical disc. Binary digital data is recorded on the optical disc according to a period when the recording mark is formed (mark period) and to a period when the recording mark is not formed (space period).
A known method for forming a recording mark on an optical disc is such that a recording mark with a recording mark length nT based on a modulation law of a recording mark length is formed using (n-1) recording pulses or (n-2) recording pulses. However, in a case where recording velocity is increased (in a case of high velocity recording), this recording method requires more amount of recording laser power (recording power) and cannot secure a sufficient width of a recording pulse. Therefore, the recording method is not appropriate for high velocity recording.
On the other hand, a known recording method suitable for high velocity recording is a controlling and recording method of laser pulse in which each of recording marks with recording mark lengths of 2T to 8T (T: cycle of channel clock) are formed using one recording pulse, as illustrated in FIG. 15. The controlling and recording method is advantageous in that a pulse width of a recording laser pulse is more easily secured and a recording power may be relatively low compared with the recording method in which (n-1) recording pulses or (n-2) recording pulses are used.
Further, Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-355809 (Tokukai 2004-355809; published on Dec. 16, 2004)) discloses a recording method capable of controlling the shape of a recording mark, in which method the number of recording pulses and a resting period are changed according to a mark length of a recording mark. Patent Document 1 describes a method in which a recording mark of 5T or less is recorded (recording mark is formed) using one recording pulse, whereas other recording mark (recording mark of 6T or more) is recorded using two or more recording pulses while changing a resting period according to a mark length of the recording mark.